Debt of Ages

Alternate history of what would have happened if King Arther hadn't died, and meddling by future and far future humans to help save the future of this world against non-human aliens of the first two books. From the back cover of the Baen first edition: "King Arthur saved the galaxy, now who will save the Once and Future King? In The Disinherited we learned that We Are Not Alone, but share this galaxy with the most loathesomely aggressive communal aliens imaginable. Thank God for the U.S. Space Force. In Legacy we learned that time-travel is not only possible for humans of the far future, it's easy. But meddling in time can have awful consequences for mere mortals:Thank God for King Arthur. And now... The Once and Future War Duke of the Britons has been saved - and as a special military consultant to the galactic overlords he has given the future new hope. But now that he has saved the universes, who shall save the King?"